1. Field of the Invention
This invention relates generally to diagnostic apparatus and methods in gynecology, and more particularly to clinical diagnosis of stress incontinence.
2. Prior Art
(a) Causes of Incontinence--Inability to deter the flow of urine from the bladder is a common phenomenon in women, particularly older women. Such inability to contain urine is termed "incontinence." Roughly half of elderly women are incontinent.
An incontinent women usually has an adequate reservoir (the bladder) for urine, but the biological "valve" is for one or another reason inadequate to prevent discharge of urine. The "valve" that normally performs this function is the urethra--the duct through which the bladder is normally emptied during urination--in conjunction with the muscle or sphincter that surrounds the urethra.
The most frequently encountered causes of incontinence in women may be classified as pathogenic, anatomical and neurological. Before incontinence in a particular women is treated, its cause must be ascertained. Not only is appropriate treatment for each kind of incontinence ineffective against other kinds of incontinence, but in some instances appropriate treatment for one type is counterproductive with respect to other types.
Incontinence that is pathogenic--caused by infection--is readily identified in ways that are outside the primary scope of my invention. (As will be seen, my invention is compatible with procedures for checking the possibilities of pathogenic incontinence.)
Anatomical and neurological incontinence, however, are readily contused by diagnosticians.
Distinguishing between them historically has been attempted by direct observations, and very recently has been accomplished by sophisticated instrumentation. Both of these systems will be described below. Unfortunately the direct observations are subject to several obstacles and inaccuracies, whereas the instrumentation is subject to such extremely high cost as to be accessible only to medical centers (as distinct from individual clinicians)--and even so is not free from certain inaccuracies and other disadvantages.
To understand the shortcomings of these methods it is necessary to understand the behavior and causes of anatomical and neurological incontinence. Both of these types appear in response to bodily stress, and particularly as reactions to a relatively abrupt increase in pressure within the abdomen.
(Traditionally the anatomical type of incontinence has been identified as "genuine stress incontinence" though both of these two types are in fact triggered by stress, and it may therefore be more accurate to describe both as, at least, "stress incontinence.")
A cough, sneeze or laugh is often the stimulus for such a pressure increase, but in more advanced stages of incontinence the patient may be unable to contain her urine even against pressure increases such as are incurred through light exercise: lifting, bending down, running, or even merely walking. Since these sorts of stress are basic to everyday living and use of the body, it will be apparent that advanced stress incontinence is virtually debilitating. Patients in which such conditions are untreated must resort to adult-size diapers or other cumbersome, relatively unsanitary, and potentially embarrassing appliances.
Stress-induced pressure increases, in normal women as well as women suffering from both types of stress incontinence, are transmitted to the bladder (though by different mechanisms), causing the pressure within the bladder to rise. In normal women, however, the pressure incurred by coughing, exercise, and so forth is exceeded by the pressure within the urethra.
When normal individuals are not urinating, the urethra is held closed by voluntarily controlled musculature (the sphincter surrounding the urethra), with the aid of surrounding anatomical structures. This musculature and other anatomical features produce a pressure within the urethra that exceeds any pressure ordinarily produced by stresses (pressures) transmitted to or arising in the bladder.
The higher pressure within the urethra stands off the liquid stored in the bladder, preventing the liquid from being discharged through the urethra and thereby out of the body.
There are primarily two ways in which this normal control system can fail: (1) the muscles and the structure that normally hold the urethra closed can become weak, and (2) the body can malfunction in such a way as to amplify the pressure increase within the bladder. In either of these abnormal situations, the pressure within the urethra is insufficient to stand off the pressure in the bladder--and urine is forced outward from the bladder through the patient's urethra.
The first of these two kinds of failure is due to anatomical weakness: the bladder opening at the top of the urethra, and the inner (or proximal, in medical terminology) end of the urethra has lost its support. This weakening probably occurs either as a result of childbirth or as part of the general deterioration of bodily structures with advancing age, or both. The inner end of the urethra, in any event, undergoes "prolapse"--it falls down or slips from its normal position.
The resulting phenomena may be viewed in a relatively mechanical way: a sudden increase in pressure within the abdomen (as with a cough) is transmitted to the bladder, and bladder pressure becomes greater than urethral pressure. Urine is then forced outwardly through the urethra.
This is known as "genuine stress incontinence." It can be treated surgically, but not by administration of medicines.
The second of the two kinds of failure enumerated above, the amplification of the stress-induced pressure increase, can occur in a woman whose urethral pressure is ample to withstand the abdominal pressure increase that is directly associated with a cough, sneeze, laugh, or even vigorous exercise. In this second kind of incontinence, however, the increased pressure within the bladder triggers nerve signals, and these nerve signals abnormally stimulate the bladder to contract. The contraction of the bladder in turn raises the pressure within the bladder very severely--to a level considerably greater than that produced directly by the stress.
The nerve signals triggered by the original pressure increase in the bladder may travel to the brain, causing return signals to the bladder along nerve paths normally used by the patient to squeeze the bladder and thereby help expel urine from the bladder. It is also possible that the nerve signals cause a more-localized chain reaction of spasms that eventually return to squeeze the bladder. Whatever the specific mechanism, this type of incontinence is characterized by a time delay of at least three to five seconds, and sometimes as long as fifteen to twenty seconds, between the originating stress and the responding contraction and discharge. In addition to the difference in timing, this type of incontinence also is usually characterized by a greater volume of discharge.
This type of stress incontinence is often called "bladder instability." It can be treated by administration of medicines, but not by surgery. In fact, attempts to correct it surgically often result in aggravating the condition.
(b) The "Stress Test"--A historically common method of determining which type of incontinence a woman has is the so-called "stress test" introduced by Doctors Bonney, Marshall and Reid. In the stress test the patient's bladder is filled with fluid (often a quarter of a liter of salt solution) and she is asked to cough. If fluid is discharged from her urethra immediately, the patient is diagnosed as suffering from "genuine stress incontinence" and requiring surgery, whereas if there is a delay the patient is diagnosed as having "bladder instability" and requiring medication. The test of course relies upon the difference in timing between the two kinds of reaction. Unfortunately this so-called "stress test" is flawed in several ways.
First, about half of incontinent women are continent when lying down. This fact results from the force of gravity on fluid in the bladder and on other bodily organs near the bladder. In a standing patient the proximal end of the urethra is essentially at the bottom of the pool of fluid in the bladder, and gravity adds substantially to the stress-induced pressure at the proximal end of the urethra. Furthermore, the weight of organs that are above the bladder tends to be applied to the bladder when the patient stands.
When the patient reclines, however, the rotation of the bladder and surrounding structures places the proximal end of the urethra much closer to the upper surface of the fluid in the bladder, or even above the upper surface, so that gravity makes no substantial addition to the stress-induced pressure at the proximal end of the urethra. At the same time there are fewer organs disposed to press upon the bladder wnen the patient reclines.
Hence the test must be conducted with the patient standing. Unfortunately, however, it is very undesirable to perform such a test with the patient standing. The standing patient will not generally be able to spread her legs sufficiently to allow the diagnostician a clear view of the distal (outer) end of the urethra. Consequently the diagnostician usually inserts her or his fingers within the patient's labia (the folds of flesh covering the vaginal outlet) to determine when that area is wetted by discharge of fluid. Under such conditions it is extremely difficult to accurately determine the timing of the discharge relative to the stress, especially considering that in some patients suffering from bladder instability the time delay is only three seconds.
Secondly, in a setting such a doctor's office the patient is often anxious. This often causes the voluntary sphincter of the urethra to go into involuntary spasm (that is, to squeeze the urethra shut), which obstructs the flow of fluid from the bladder. It has been shown that one-third or more of incontinent women may be unable to demonstrate incontinence under these circumstances. After leaving the doctor, however, the patient may again become incontinent.
This problem is aggravated by the fact that the patient must stand during the test, essentially confronting the doctor, with the doctor's fingers placed within the patient's labia. This confrontation accentuates the patient's realization that any fluid lost will wet the doctor's fingers, and such behavior of course contradicts all normal social schooling. As a result, in addition to the involuntary anxiety spasm discussed in the preceding paragraph, many patients may actually consciously squeeze the urethral sphincter more forcefully than they may normally squeeze during coughing, sneezing, exercising, etc.--thereby defeating the test.
Thirdly, many women have relatively large labia, which can act as a dam to discharge of fluid from the urethra. This effect makes it very difficult to determine whether fluid from the bladder is lost immediately or after a delay.
Fourthly, many women are obese, and the compound obstructions formed by rolls of flesh and folds of skin at the thighs of an obese patient similarly dam the fluid emerging from the urethra. The timing determination is accordingly impeded.
Fifthly, in any observation of biological phenomena there is a certain amount of imprecision. Diagnosticians may find that a discharge occurs with a seeming delay of one or two seconds, which does not correspond neatly to either category of stress incontinence. Similarly diagnosticians may find that some discharge occurs immediately after stress, and that an additional discharge "seems" to occur later. It must be realized that some women suffer from both types of incontinence, which would account for a dual discharge, but it is extremely difficult to determine reliably that a second discharge has occurred after the labia and the diagnostician's fingers are already wetted.
(c) Other Direct Observations--Partly as a result of the difficulties just described, diagnosticians usually perform other tests to gather additional information on the patient's anatomical condition. In particular, one common test--familiarly known as the "Q-tip test"--involves inserting a "Q-tip" cotton swab partway into the urethra, while the patient is lying on her back in the customary pelvic-examination position, and instructing the patient to bear down (as in defecation). In these circumstances the swab initially is generally horizontal, and deflects upward when the patient bears down.
In a normal patient the upward deflection does not exceed roughly thirty degrees. In the abnormal anatomical condition that gives rise to so-called "genuine stress incontinence," however, the upward deflection can approach ninety degrees. Since many diagnosticians are accustomed to including this test in their "work up," it is desirable to ensure that any new procedure proposed is compatible with--or, preferably, facilitates--some version of the "Q-tip test."
Similarly, it is generally routine to take a sample of urine directly from the patient's bladder. Such a sample is helpful in checking for pathogenic conditions, since it is less likely than an excreted sample to be contaminated by chance unsanitary conditions within or just outside the patient's labia. Consequently in any new procedure the obtaining of such a sample should be facilitated.
(d) Modern Instrumentation--The ambiguities in the now-classical "stress test" have led to introduction of electronic instrumentation for determining pressure relationships between the bladder and the proximal end of the urethra.
Such instrumentation generally consists of (1) a first pressure sensor that is inserted entirely through the urethra into the bladder, to sense the pressure within that organ; (2) a second pressure sensor that is inserted partway through the urethra, to sense the pressure along that duct, and (3) electronics and display devices for determining and recording those two pressures as they change with time, and in some instruments for also determining and recording certain relationships between those pressures.
The pressure sensors used may be of two different types. First, a pressure sensor may consist of (a) a small transducer, positionable within the bladder or urethra, that controls an electrical resistance or an electrical voltage source--together with (b) electrical leads for directing to the exterior of the body electrical signals related to the sensed pressure, and (c) a rod or the like for inserting the transducers and leads into position, and holding them in position, for measurement.
The other type of pressure sensor may consist of (a) a pair of tubes inserted into the bladder and urethra respectively, and (b) pressure-measurement devices attached to the ends of the tubes that are outside the body, to measure the pressure transmitted through the tubes while the tubes are held in position. With this type of sensor, the tubes are usually provided in the form of a single tube structure with parallel channels within it, and separate openings spaced along the tube near its proximal end.
In use of these instruments, the pressure sensors (of either type) are inserted together into the urethra while the patient reclines in the usual pelvic-examination position. One sensor is advanced approximately two to three inches forward of the other sensor, while the instrument operator observes the changing pressure readouts from the instrument. When the readout from the forward or proximal sensor decreases (indicating that the sensor has passed from the urethra into the bladder) but the readout from the rearward or distal sensor remains higher (indicating that this sensor has not yet reached the bladder), the insertion is stopped and data are taken.
In one very expensive unit, the instrument operator advances the sensor pair into the urethra and bladder, and then the apparatus (rather than the operator) automatically withdraws the catheter at a regular velocity, while measuring and recording the pressure relationships between bladder and urethra.
In other parts of the diagnosis the patient is instructed to cough, laugh, exercise, or otherwise incur abdominal stress, and the sensor measurements are recorded as they respond to the stress.
Instruments of this type are operationally preferable to the "stress test." The sensors can be emplaced while the patient is lying down and are relatively unintrusive, making insertion fairly easy.
Because, the apparatus is very sensitive and relies upon pressure measurements rather than actual discharge of urine, it appears from the literature that for some patients the entire test can be successfully (that is, accurately) conducted while the patient reclines.
Yet modern instrumentation for stress-incontinence diagnosis is unsatisfactory in at least four ways:
First, there remains a very large fraction of the population of incontinent patients whose incontinence is masked by the patients' lying down.
Secondly, the equipment is prohibitively expensive for use by individual clinicians. The cost for one operational device ranges roughly from $7,000 to $50,000, depending upon the degree of automaticity desired. Modern medical philosophy, however, for very good reasons favors acquiring as much information as possible in the doctor's office, rather than in the hospital or large-scale medical center.
Although this instrumentation has found an effective market among high-volume diagnostic laboratories such as those found in medical centers, even as evaluated by these facilities such an instrument is inordinately expensive.
Thirdly, its operation is surprisingly time-consuming, requiring generally an hour to an hour and a half for full diagnosis of each patient--though only a part of this time is occupied by the actual testing. This inordinate consumption of time is wearing on the patient, and also is expensive in terms of laboratory personnel.
Fourthly, many a patient (particularly among the elderly) finds it personally degrading or offensive to have her genital region connected to a machine. This is particularly true if a cost-conscious technician, having set up the test, goes off to tend to other business--leaving the patient to lie for an hour with wires trailing from her vulva to a box of electronics. Resulting psychological effects can disturb the measurement.
Finally, in a relatively small number of patients, the tube or rod used to advance the forward sensor into the bladder may irritate the opening of the urethra into the bladder, and this irritation may cause spurious indications from the instrumentation. In particular, such irritation may have a slight tendency to produce an emulation of bladder instability, or to suppress an already existing tendency toward bladder instability. On the other hand, such irritation may also have some very slight tendency to stimulate the urethral sphincter to close either more or less forcefully than it customarily does--thereby either suppressing or emulating the observable characteristics associated with genuine stress incontinence.
Although this last-mentioned set of problems is not a major drawback, it is of some interest in relation to my invention, as will be seen.
(e) Externally Stabilized Catheter--Doctors Sutherst and Brown of the University of Liverpool have described their studies of incontinence diagnosis making use of a two-channel catheter with a proximal end of one channel positioned within the urethra. 34 Urologia Internationalis 403 (1979), 52 British Journal of Urology 138 (1980), 53 British Journal of Urology 360 (1981).
In some of these studies the catheter was stabilized to the exterior of the patient's body to "prevent movement due to its weight and connections". The stabilization was accomplished by means of a "spring paper clip fixed to a flexible ring pessary . . . held between the patient's thighs".
Although these studies offered favorably high correlations between observed liquid discharge and other indications of "genuine stress incontinence," the experimental arrangements were in several ways marginal from the viewpoint of an individual clinician. The external appliance worn by the patient to stabilize the catheter would produce considerable patient discomfort if the patient were to bend, stretch, or even walk, since the urethral meatus in particular (which would be abraded by such activities) is very sensitive. Consequently in the studies described the patient could only be "tilted to the erect position on a motorised bed." Such an apparatus, of course, is far beyond the scope of equippage for the vast majority of individual clinicians.
In addition, the appliance would tend to fix the rearward end of the tube too securely to the patient's body, preventing effective incorporation of the "Q-tip test" into the diagnostic apparatus and method. As will be apparent, all of these limitations would very severely limit the feasibility of the published method for practical everyday clinical use.
(f) Appliances Used in Other Procedures--The foregoing discussions encompass prior approaches to diagnosis of stress incontinence. Certain prior-art devices used in other medical procedures, however, are related to my invention and bear mention here.
One of these devices is a catheter tube. Catheters are slender but strong tubes, usually flexible, used for innumerable purposes in medicine, and particularly in investigation of the urinary tract and virtually all other bodily cavities. They have been used in prior methods for incontinence diagnosis in three ways.
First, they are generally used to take urine samples from within the bladder as previously mentioned--principally for investigation of pathogenic incontinence, as distinguished from stress incontinence. Secondly, as previously mentioned they are used in some of the instruments described above to transmit bladder and urethral pressure to pressure gauges outside the patient's body. Thirdly, as previously mentioned, catheters are proposed in one known system for stress-incontinence diagnosis, involving stabilization of a catheter to the patient's thighs.
Catheters are made from a great variety of materials, but generally speaking the materials are selected and processed for smoothness and relative stiffness of the finished product--so that the catheters can be slid smoothly through the body openings or ducts of interest. Thus elastomeric catheters are generally manufactured with durometer (an industrial measure of hardness) between seventy and ninety.
Also as a general rule catheters are long enough to pass into the body organ or vessel of interest, and if a catheter is longer than necessary to satisfy this condition, the excess length is of no consequence.
Another relevant device is a bougie (usually pronounced "BOO-zhee"). It is a generally cylindrical instrument or article, sometimes tapered, for insertion into a tubular passage of the body. Bougies have a variety of purposes, not previously including diagnosis of incontinence. Prior-art bougies have been solid, in the sense that they have not had apertures formed in them.
One kind of bougie is known in medicine as a "lamineria." It is a small piece of extremely hygroscopic (water absorbent) material--essentially a super-sponge. One kind of lamineria is inserted into the cervix or mouth of a woman's uterus in preparation for childbirth, to remove water from the tissue there. Originally a lamineria was made from a particular species of seaweed, but more recently an artificially made polyvinyl-alcohol sponge has been used. In cervical dilators the polyvinyl-alcohol sponge is generally impregnated with synthetic magnesium sulfate to enhance, and particularly to accelerate, the absorption and expansion.
The object of such a lamineria is to remove naturally occurring moisture. Incidentally to that object the lamineria swells very substantially as it takes up water. Such devices have not been used in diagnosing incontinence.